diff --git a/ApplicationCode/ReservoirDataModel/RigActiveCellInfo.cpp b/ApplicationCode/ReservoirDataModel/RigActiveCellInfo.cpp
index 1a27ad8c62..9354aea2ba 100644
--- a/ApplicationCode/ReservoirDataModel/RigActiveCellInfo.cpp
+++ b/ApplicationCode/ReservoirDataModel/RigActiveCellInfo.cpp
@@ -162,7 +162,7 @@ void RigActiveCellInfo::IJKBoundingBox(cvf::Vec3st& min, cvf::Vec3st& max) const
 //--------------------------------------------------------------------------------------------------
 /// 
 //--------------------------------------------------------------------------------------------------
-void RigActiveCellInfo::gridActiveCellCounts(size_t gridIndex, size_t& activeCellCount)
+void RigActiveCellInfo::gridActiveCellCounts(size_t gridIndex, size_t& activeCellCount) const
 {
     activeCellCount = m_perGridActiveCellInfo[gridIndex].activeCellCount();
 }
diff --git a/ApplicationCode/ReservoirDataModel/RigActiveCellInfo.h b/ApplicationCode/ReservoirDataModel/RigActiveCellInfo.h
index 93c23ba12a..87a9224f9f 100644
--- a/ApplicationCode/ReservoirDataModel/RigActiveCellInfo.h
+++ b/ApplicationCode/ReservoirDataModel/RigActiveCellInfo.h
@@ -46,7 +46,7 @@ public:
 
     void                setGridCount(size_t gridCount);
     void                setGridActiveCellCounts(size_t gridIndex, size_t activeCellCount);
-    void                gridActiveCellCounts(size_t gridIndex, size_t& activeCellCount);
+    void                gridActiveCellCounts(size_t gridIndex, size_t& activeCellCount) const;
     void                computeDerivedData();
 
     void                setIJKBoundingBox(const cvf::Vec3st& min, const cvf::Vec3st& max);